1. Field of the Invention
The present invention relates to a process for the spinning and spooling of preoriented polyester filaments comprising polybutylene terephthalate (PBT) and/or polytrimethylene terephthalate (PTMT) (preferably of PTMT) in an amount of at least 90 weight % relative to the total weight of the polyester filament. The present invention also relates to and comprises preoriented polyester filaments that can be obtained by means of the process. In addition, the present invention relates to a process for the stretch texturing of the spun and spooled polyester filaments, as well as the bulky polyester filaments that can be obtained by means of stretch texturing.
2. Summary of the Related Art
The production of continuous polyester filaments, particularly polyethylene terephthalate (PET) filaments, in a two-stage process, is known in the art. In these processes, flat, preoriented filaments are spun and spooled during a first stage and subsequently, during a second stage, stretched into finished form and thermofixed, or else stretch-textured into bulky filaments.
xe2x80x9cSynthetic Fibersxe2x80x9d (F. Fournxc3xa9 (1995), published by Hanser-Verlag, Munich) provides an overview of this. Only the production of PET fibers is described there, and no closed spinning technology is explained. Rather, only an overview of the general characteristics are described.
The technical production of various spinable polymers, such as polypropylene, polyamides, polyesters, etc., among others, is the object of application DE-OS 38 19 913. Only the production of PET fibers is described in the examples, as these can be obtained at the temperature at which the polymer is processed.
A problem in the production of continuous polytrimethylene terephthalate (PTMT) or polybutylene terephthalate (PBT) filaments is that preoriented filaments have a considerable tendency to shrink during storage at ambient temperature, both immediately after spinning and upon spooling, as well as several hours after the spooling, leading to shortening of the fibers. The bobbin is thereby compressed so that, in the extreme case, a tight shrinking of the bobbin on the spooling chuck can arise, and the bobbin can no longer be removed. Furthermore, a so-called xe2x80x9csaddlexe2x80x9d with hard edges and an indented middle is formed in the bobbin. Consequently, the characteristic textile values of the filaments, such as the uster, for example, become unevenly stronger, and there are unspooling problems during the processing of the bobbins. Only the limitation of the weight of the bobbin to less than 4 kg provides remedies this. Such problems do not appear during the processing of PET fibers.
Furthermore, it has been observed that, in contrast to PET filament, preoriented PBT- or PTMT filaments age to an increased degree during storage. A structural hardening appears, which leads to such a great reduction in filament shrinkage that a subsequent crystallization can be observed. Such types of PBT and PTMT filaments are only conditionally suitable for further processing as they lead to errors in stretch texturing as well as to a significant reduction of tenacity of the textured thread. The reduction of the texturing speed or of the stretching ratio is the result.
These differences between PET and PBT or PTMT are attributable to structural differences and differences in characteristics such as are presented, for example, in Chemical Fibers Int., page 53, volume 50 (2000) and that were the theme of the 39th Int. Man-Made Fibers Congress, from Sep. 13 to 15, 2000, in Dornbirn. It is assumed that different chain formations are responsible for the differences in characteristics.
First attempts at the solution of these problems are described in WO 99/27168 and EP 0 731 196 B1. WO 99/27618 discloses a polyester fiber consisting of at least 90 weight % polytrimethylene terephthalate and has a boiling-water shrinkage of between 5%, and 16%, as well as an elongation of 20% to 60%. The production of polyester fibers described in WO 99/27168 is carried out by means of spinning and stretching. In this, spinning speeds of a maximum of 2100 m/min. are stated. The process is uneconomical because of the low spinning speed. Furthermore, the polyester fibers that are obtained are, as the indicated characteristic parameters show, strongly crystalline and are, as a result, only suitable for stretch texturing processes to a limited extent.
EP 0 731 196 B1 claims a process for spinning, stretching, and spooling synthetic thread in which the thread is, after the stretching but before the spooling, subjected to heat treatment to reduce the tendency to shrink. Usable synthetic fibers also include polytrimethylene terephthalate fibers. In accordance with EP 0 731 196 B1, the heat treatment is applied as the synthetic thread is guided closelyxe2x80x94but essentially without contactxe2x80x94along a longitudinally extended heating surface. The heat treatment makes the process more expensive and additionally results in synthetic threads having high crystallinity that are for stretch texturing to a limited extent.
The stretch texturing of preoriented polytrimethylene terephthalate filaments at texturing speeds of 450 m/min. and 850 m/min. is described in the article by Dr. H. S. Brown and H. H. Chuah, xe2x80x9cTexturing of textile filament yarns based on polytrimethylene terephthalatexe2x80x9d, in Chemical Fibers International, Volume 47, Feb. 1997, pages 72-74. According to this disclosure, the lower texturing speed of 450 m/min. is better suited for polytrimethylene terephthalate filaments, since fibers with better material characteristics are obtained in this case. The tenacity of the polytrimethylene terephthalate fibers is reported to be 26.5 cN/tex (texturing speed of 450 m/min.) or 29.15 cN/tex (texturing speed of 850 m/min.), respectively, and the elongation 38.0% (texturing speed of 450 m/min.) or 33.5% (texturing speed of 850 m/min.), respectively.
WO 01/04393 describes PTMT filaments that have a shrinkage in the range of 3 to 40%. This value was determined immediately after the production of the filaments, however. As FIG. 1 of the present specification shows, this value drops to below 20% under normal conditions after a storage time of 4 weeks.
Shrinkage is a measure of the processability and the degree of crystallization of the fibers. The fibers described in WO 01/04393 have a higher degree of crystallization, resulting in significantly worse processing and only at lower stretching ratios and/or texturing speeds.
The present invention provides a simplified process for spinning and spooling preoriented polyester filaments comprising (by at least 90 weight % relative to the total weight of the filaments) PBT and/or PTMT. The preoriented polyester filaments made according to the method of the invention have values of elongation at break in the range of 90% to 165%, high uniformity of the filament characteristic values, and a low degree of crystallization.
The process of the invention also can be conducted on large scale and economically. The process in accordance with the invention permits the highest possible spinning speeds, preferably greater than 2200 m/min., and high thread weights (of more than 4 kg) of the bobbin.
The present invention also improves the storability of the preoriented polyester filaments obtained by means of the process of the invention. Filaments made according to the process of the invention can be stored for a longer period of time, such as 4 weeks. Compression of the bobbin during storage, particularly tight shrinking of the bobbin onto the spooling chuck, as well as the formation of a saddle with hard edges and indented middle part, is prevented, to the extent possible, so that problems of unspooling during the further processing of the bobbins is eliminated.
In accordance with the invention, the preoriented polyester filaments can be further processed, in a simple way, in a stretch or stretch texturing process, particularly at high texturing speeds, preferably greater than 450 m/min. The filaments obtained by means of stretch texturing have outstanding material characteristics, such as a high tenacity at break of more than 26 cN/tex, as well as high elongation at break of more than 30% in the case of HE-filaments, or more than 36% for SET filaments, respectively.
All patents, patent applications, and other publications recited herein are incorporated by reference in their entirety. In the event of an inconsistency between the present disclosure and the disclosures incorporated by reference, the present disclosure is relied upon herein.